Over-voltage protection techniques



July 25, 1967 o. WANASELJA 3,333,153

OVER-VOLTAGE PROTECTION TECHNIQUES Original Filed Aug. 31, 1964 5Sheets-Sheet l FIG.'|

INVENTOR. OLEY WANASELJA TTORNEYS y 5, 1967 o. WANASELJA 3,333,153

OVER-VOLTAGE PROTECTION TECHNIQUES Original Filed Aug. 31, 1964 5Sheets-Sheet 2 F IG."3

FIG."4

INVENTOR. OLEY WANASELJA Z/l/l/J j/l/ BY fi F Q AMM a IM ATTORNEYS July25, 1967 o. WANASELJA OVER-VOLTAGE PROTECTION TECHNIQUES Original FiledAug. 51,1964

5 Sheets-Sheet 3 INVENTOR.

OLEY WANASELJA BY Wmqau, FMQaambNkm? P ATTORNEYS y 1967 o. WANASELJA3,333,153

OVER-VOLTAGE PROTECTION TECHNIQUES Original Filed Aug. 51, 1964 5Sheets-Sheet 5 207 200 n\\ \W W j fzo/ mm 6/; 2 a. I 7 o v is FIG. oINVENTOR.

OLEY WANASELJA- BY il lorqwu hmqq: ,burkw v.2

TTORNEYS United States Patent 10 Claims. (Cl. 317-9) ABSTRACT OF THEDISCLOSURE A discharge type over-voltage protector employing electrodesin a gas filled cylinder or cartridge configuration is disclosed herein,together with the method of manufacturing same.

This application is a division of application Ser. No. 393,257, filedAug. 31, 1964 and now Patent No. 3,284,625.

This invention relates to apparatus and methods for protecting equipmentfrom over-voltage conditions and is particularly directed toover-voltage sensitive devices for attachment to electrical conductorsserving various types of apparatus, for example, communicationequipment. In an illustrative application the protection device servesthe purpose of protecting the equipment from the effects of excessivevoltage such as might occur because of a fault, contact by high tensionline, lightening and the like.

Of the various types of equipment presently employed for accomplishingthe foregoing, each suffers from one or more disadvantage includingexcess size and cost, hazardous conditions during servicing,less-than-optimum reliability, maintenance difficulties, and loss offunction in presence of sustained overload.

It is an object of the invention to overcome or substantially reduce theforegoing shortcomings and to this end the invention providesimprovements in construction and performance leading to reductions insize and cost, simplifications in servicing, reduction in hazards, andan increase in reliability. Moreover, in the techniques according to theinvention, additional protection features are attained withoutsignificantly impairing the essential simplicity of construction.

These and other objects and advantages of the inven tion will be setforth in part hereinafter and in part will be obvious herefrom, or maybe learned by practice with the invention, the same being realized andattained by means of the instrumentalities and combinations pointed outin the appended claims.

The invention consists in the novel processes, methods, steps, parts,combinations and improvements herein shown and described.

Serving to illustrate exemplary embodiments of the invention are thedrawings of which:

FIGURE 1 is an elevational cross-sectional view of one arrangementaccording to the invention;

FIGURE 2 is an isometric detail view illustrating components of thedevice of FIGURE 1;

FIGURE 3 is an end elevational view partly in section of the protectionarrangement of FIGURE 1; 1

FIGURE 4 is a plan view, partly in section, taken along the lines IV-IVof FIGURE 1;

FIGURE 5 is a plan view, partly in section, of an alternate embodimentand is taken along the lines VV of FIGURE 6;

FIGURE 6 is an elevational view, partly in section, of the embodiment ofFIGURE 5;

FIGURE 7 is a view taken along the lines VIIVII of FIGURE 6;

FGURE 8 is a view taken along the lines VIIIVIII of FIGURE 6;

3,333,153 Patented July 25, 1967 "ice FGURE 9 illustrates in isometricview, an over-voltage sensing element according to the invention;

FIGURE 10 illustrates the element of FIGURE 9 in an elevationalsectional view; and

FIGURE 11 is a schematic diagram illustrating the combination of theover-voltage element of FIGURES 9, 10 with an air-gap type protector.

Referring to the embodiment of FIGURES 1-4, the arrangement thereinillustrated comprises a housing assembly 10 which includes a snap-oncover 11 and a base 12. The housing assembly is illustrativelyconstructed of Bakelite, is preferably weatherproof, and base 12 thereofincluding mounting pads 14 and 15.

Base 12 is provided wit ha shoulder portion 16 which receives theperiphery of cover 11. The shoulder portion of the base also includesdetents 17 for providing a releasable assembly of the cover to the base.The cover also includes finger grips 18 for facilitating diassembly.

Mounted on the base in aligned relationship and secured by suitablemeans are a pair of clips 20 each formed of spaced blades 20A and 20B.See FIGURE 2. Each clip 20 also includes an integral extension 21, tothe distal end of which is secured by suitable means a terminal screw22. The terminal screws are each adapted to mechanically andelectrically connect one of the lines to be protected with therespective clip-20 via an associated lead (not shown) which is routedinside the assembly 10* and joined to the respective terminal screw. Theclips 20 may be made of any suitbale material; Phosphor bronze, springbrass or beryllium copper are satisfactory.

The clips 20 are aligned to receive the over-voltage element 25. In theembodiment illustrated in FIGURES 1-4, this over-voltage element is ofknown construction, being for example, an AEI type 16 gas tubeprotector. A cartridge of this type comprises a gas filled housinghaving a pair of opposed, spaced electrodes each of which makeselectrical contact with one of the cartridge end contacts 25A and 25B.In the presence of an excessive voltage the gas between the electrodesis ionized thereby eifectively shorting the end terminals 25A, 25B andconnecting them to the case of the protector and to external ground asdescribed below. The lines and equipment connected to these electrodesvia the clips 20 are thus also short-circuited to thereby prevent theover-voltage condition from causing excessive current flow in theprotected apparatus. Described more fully hereinafter in connection withFIGURES 9 and 10 is a gas-filled protector designed according to theinvention.

Secured to cover 11 as by being press fitted thereto or molded thereinis a ground stud .30 having an external threaded end 30A which isadapted to be electrically connected with a convenient ground potentialpoint. The

stud passes through the top of cover 11 and the interior end 303 thereofis connected, as by a rivet or by swaging, to a center clip 31 which isconstructed of spaced fingers or blades 31A, 31B which resiliently gripthe center portion of the over-voltage cartridge 25. The clip 31 isdesigned with a resilience which grips the cartridge 25 with a greaterforce than that which is provided by the end clips 20. By thisrelationship, a removal of the cover 11 automatically carries with itthe cartridge 25 since the excessive grip of the center clip 31 causesthe element 25 to be pulled from the clips 20 in the act of pulling thecover 11 from the base 12.

This arrangement provides an important feature of safety and ease ofmaintenance in the replacement of the cartridge. It may be seen thatwith cover 11 separated from base 12, the Serviceman can safely andeasily insert a new cartridge in the center clip 31 since it is isolatedfrom the energized end clips 20. Hence the serviceman is not required toget close to the energized points but rather may work completely remotefrom these points. The safety aspect and functionality of thisarrangement becomes particularly apparent when it is recalled that theremoval of a defective cartridge from a hot circuit frequently requiresspecial too-ls and, of course, must be done with extreme caution.

In the case of a prolonged over-voltage condition, there is apossibility that the gas tube or other protective element will fail. Ifthe element becomes an open circuit, the equipment and lines connectedthereto are no longer protected. To eliminate this possibility and toprovide an extra measure of reliability and safety, the embodiment ofFIGURES 14 includes a shorting arrangement described below.

Mounted in spaced relationship above the cartridge and clip assembly isa shorting bar 40 (see FIGURE 2) having a center bridge section 40A anda pair of sidewalls 43, forming with the bridge an inverted, generallyU-shaped structure. The distal ends of the sidewalls 43 include channelshaped contactors 44 extending away from the sides and parallel with thecenter section 40A. It may be noted that the contacting sections 44 areeach in spaced alignment with a respective end clip and it may befurther noted that the channel shape of the contactors 44 is such as toprovide an effective electrical and resilient contact with therespective clip in the event that the shorting bar is depressed asdescribed hereinafter.

The bridge section 40A includes a central bore 41 through which theground stud passes so that the shorting bar is slidable on the stud.

Coaxial on the stud is a spring 50, the lower end of which bears againstthe bridge section tending to urge the shorting bar against the clips20. This action is resisted by an assembly which includes a U-shapedretainer 51 and fusible spacer 55.

The sides 52 of retainer 51 each include bent tongues 53 which extendinto respective holes 42 in the bridge of shortin bar 40. The centersection 51 of the retainer clip has secured thereto the fusible spacer55 which depends from the center section and is secured thereto byappropriate means such as rivets or screws. The spacer 55 has its distalend abutting the center section of the cartridge 25. It may be seen thatthe tendency of spring 50 to push the shorting bar against the clips 20is resisted by the retainer 51 and the fusible element.

In the presence of a prolonged surge which is sutficient to fuse thespacer 55, the spring 50 will thrust the shorting bar 48 downward sothat the contactors 44 thereof contact the clips 20. When this occurs, afurther direct short-circuit is established between the clips andbetween the lines connected thereto. Moreover, all of these points aregrounded via lug 30. By this arrangement a sustained over-voltagecondition which might otherwise burn out the protective cartridge 25,produces a supplementary shorting and grounding action. Hence, theequipment is protected even in the presence of sustained over-voltageconditions. Furthermore, its is grounded.

As in the case of removal of cartridge 25, the abovedescribedarrangement facilitates the replacement of the shorting bar and relatedassembly since this assembly is connected to the cover 11 and is removedfrom the area of the energized clips when the housing cover 11 isremoved Furthermore, by simply compressing the U-shaped retainer 51, itmay be removed from the shorting bar 40 and replaced when the fusiblespacer 55 has been expended.

The shorting bar 40 is preferably of copper or brass composition whilethe center clip 31 is conveniently formed from Phosphor bronze, springbrass or beryllium copper. The fusible element 55 may be lead, solder,babbit or other appropriate material in accordance with ment,

installation requirements and the ratings of the protector 25, thefusible element being designed to melt when the current rating of theover-voltage tube is exceeded.

An alternate embodiment is shown in FIGURES 58. As illustrated therein,the housing includes a cover 11 adapted to be releasably engaged with abase 112, detents 117 being employed (FIGURE 8) in analogous fashion tothe detents of the first described embodiment.

Molded into the base assembly 112 are clips 120 which are designed toreceive an over-voltage tube 125, which is of the same configuration asthe corresponding tube of the previously described embodiment exceptthat an evacuation tube A is also illustrated. To allow for thisevacuation tube the clips 120 each include a slot 121.

The clips 120 are biased towards one another to provide resilientconnection with the end contact caps 1258 of the protector element.

The base portion of each clip 120 includes an integral extension 121which is molded into the base 112 and angularly disposed with respect tothe axis of the protection element 125 such that the terminal ends ofthese extensions are located in approximately diametn'c relativeposition as may be seen clearly in FIGURE 5. The end terminals areprovided with threaded studs 122 to which the wires of the circuit to beprotected are attached.

At an intermediate point on each of the integral clip extensions 121there is provided an upstanding rod 123, see FIG. 8, which is inelectrical and mechanical contact with the respective clip extension121, illustrated by swaging. The rods 123, which are molded into asection 112A of the base assembly, have their upper ends connected torespective contacts 124.

Spaced above the pair of contacts 124 is a shorting bar 140 which in theinstant embodiment is of generally rectangular shape and is disposed atright angles to the axis of the clips. The shorting bar includes acentral bore 140A through which passes a center clip 131. The latter isformed from a metal strip which is bent at its central portion toencircle the over-voltage element 125 (see FIGURE 8) and with the endsdisposed in a parallel relationship and joined to a ground stud as byrivet 130A.

Encircling the center clip 131 is a spring 150, the upper end of whichbears against the housing cover 110. The lower end abuts the shortingbar and urges the same towards the contacts 124 of end clips 120. Thetendency of spring to force shorting bar 140 into contact with contacts124 whereby the end clips and cartridge would be short-circuited andgrounded, is prevented by the action of the fusible spacer which has aroughly H shape with the center section disposed between the sides ofthe center clip 131. In the event of a prolonged over-voltage condition,the fusible pellet 155 will fuse whereupon spring 150 forces theshorting bar 140 into electrical contact with the contact surfaces 124.When this occurs the over-voltage device 125 and equipment connectedthereto are short-circuited and grounded. Of course, the initialshort-circuitry is provided by the protector 125.

The features mentioned in connection with the arrangement of FIGURES l-4apply as well to the embodiment in FIGURES 5-8. In addition the latterembodiment offers simplifications in structure which facilitate massproduction of the protection apparatus.

Referring now to FIGURES 9 and 10, there is shown therein a gas filledover-voltage protector according to the invention which may be used in asubstitution for the previously described protector, which ischaracterized by simplicity of design as well as reliability, and whichis especially amenable to low-cost, high speed, mass productiontechniques.

The over-voltage protection element of FIGURES 9 and 10 includes acylindrical metal housing 200 which is illustratively of a high nickelalloy composition. The

ends of cylinder 200 are each provided with a header including a ferrule201 which is preferably of the same composition as the cylinder.Disposed coaxially in the ferrules in sealed relation therewith areinsuiative compression seals 202 which are preferably of glass orceramic composition. The seals 202 are of annular shape and includecentral bores through which respective electrodes 203 pass. The externalends of the electrodes are provided with suitable connectors while theinterior ends are spaced by a distance which depends upon the desiredbreakdown characteristics.

In the region of the gap between the electrodes, the central section 200includes a rim section 205, the inner diameter of which is also adjustedin accordance with the desired tube rating. Thus embodied, the protectoris filled with a suitable gas, such as argon. Pressure will depend ondesired rating.

In one preferred embodiment the housing 200 is provided with a groundlug 208 which is secured to a strap 207 encircling housing 200. A groundconnection may thus be made directly to the tube housing.

The ease with which the foregoing arrangement may be produced will beapparent from the description of a typical assembly process as describedbelow.

One of the glass-metal headers is welded to the body 200 at one endthereof. The tube assembly is then evacuated at a high temperature,e.g., 300 C., to de-gas all materials. The assembly is then transferredto a dry box which typically contains dry nitrogen. The argon or otherdesired gas is injected into the dry box whereupon the tube is filledwith gas. The opposite header assembly is then induction welded to thebody 200 to complete the assembly. Testing for leaks and electricalcharacteristics then follows:

In FIGURE 11 there is illustrated the combination of the over-voltagetube of FIGURES 9 and 10 with an air-gap type protect-or such as made bythe Western Electric Company, Cook Electric Company or RelianceElectric. By choice of proper connectors on leads 203 the tube ofFIGURES 9 and 10 can be readily attached to such air gap assemblieswithout the need for modification. By this arrangement and with theprotector 200 set to breakdown before the air-gap protector, all of thebenefits provided by the gas-filled protector are added to the fail-safefeatures of the air-gap protect-or without impeding the latter.

In a typical application the striking voltage of the gasfilled tube is,say, 300 volts while the air-gap protector is adjusted for a 350-400volt rating. Hence, the gasfilled protector will always operate firstwhile the air-gap device will be activated only in the event that thegasfilled protector malfunctions.

As seen in FIGURE 11 such an assembly comprises the connection of tube200 to the line terminals 220 and 221 of an air gap protector 225. Thelatter includes two sets of spaced electrodes 230, each set forming anair-gap and being connected between one of the lines to be protected andthe ground point. The shell of tube 200 is similarly connected to theground point.

In the practice and study of the invention, modifications willundoubtedly occur to those skilled in the art. The invention is thus notlimited to the specific mechanisms and processes herein shown butdepartures may be made therefrom within the scope of the accompanyingclaims without departing from the principles of the invention andwithout sacrificing its chief advantages.

The term ceramic as used in the claims herein refers to materialscommonly referred to as ceramic and as glass.

What is claimed is:

1. An overvoltage protection discharge device comprising a generallytubular, unitary conductive casing consisting essentially of a metallicwall, a ferrule attached to each end of said casing for sealing saidcasing, each ferrule including an outer metallic sleeve, an annularceramic insulator sealed within said sleeve and an electrode extendingthrough and sealed to said insulator with its interior end spaced apredetermined axial distance from the opposing electrode.

2. A protection device as defined in claim 1 in which said casingincludes a ground terminal common to said electrodes.

3. A protection device as defined in claim 2 in which said groundterminal comprises a threaded stud secured to said casing.

4. A protection device as defined in claim 1 in which said casingincludes a reduced diameter section adjacent the spaced interior ends ofsaid electrodes, said reduced diameter having a value selected accordingto the desired breakdown characteristics of said protection device.

5. A protection device as defined in claim 1 in which said tubularcasing is cylindrical and contains a gas adapted to ionize in thepresence of excessive voltage.

6. A protection device as defined in claim 1 in which said electrodesare each generally rod shaped.

7. A protection device as defined in claim 1 including a coaxial strapsecured to said casing and a ground stud secured to and extendingradially outward from said strap.

8. A protection device comprising an overvoltage discharge elementconsisting essentially of a metallic conductive cylinder, an ionizablegas within said cylinder, a pair of electrode rods extending coaxiallyinto said cylinder from the ends thereof and spaced to form a gap, andmeans at each end of said cylinder for insulating said electrodes fromsaid cylinder and for sealing said cylinder,

References Cited UNITED STATES PATENTS 3,289,027 11/1966 Jones 3l3231MILTON O. HIRSHFIELD, Primary Examiner.

R. V. LUPO, Assistant Examiner.

1. AN OVERVOLTAGE PROTECTION DISCHARGE DEVICE COMPRISING A GENERALLYTUBULAR, UNITARY CONDUCTIVE CASING CONSISTING ESSENTIALLY OF A METALLICWALL, A FERRULE ATTACHED TO EACH END OF SAID CASING FOR SEALING SAIDCASING, EACH FERRULE INCLUDING AN OUTER METALLIC SLEEVE, AN ANNULARCERAMIC INSULATOR SEALED WITHIN SAID SLEEVE AND AN ELECTRODE EXTENDINGTHROUGH AND SEALED TO SAID INSULATOR WITH ITS INTERIOR END SPACED APREDETERMINED AXIAL DISTANCE FROM THE OPPOSING ELECTRODE.